LINQ to SQL is an O/RM
(object relational mapping) implementation that ships in the .NET
Framework "Orcas" release, and which allows you to model a
relational database using .NET classes. You can then query the
database using LINQ, as well as update/insert/delete data from it.

LINQ to SQL fully supports transactions, views, and stored
procedures. It also provides an easy way to integrate data validation and
business logic rules into your data model.

Modeling Databases Using LINQ to SQL:

Visual Studio "Orcas" ships with a LINQ to SQL
designer that provides an easy way to model and visualize a database as a LINQ
to SQL object model. My next blog post will cover in more depth how to
use this designer (you can also watch this video I made in January to see me build a
LINQ to SQL model from scratch using it).

Using the LINQ to SQL designer I can easily create a
representation of the sample "Northwind" database like below:

Figure 1

My LINQ to SQL design-surface above defines
four entity classes: Product, Category, Order and OrderDetail. The
properties of each class map to the columns of a corresponding table in
the database. Each instance of a class entity represents a row within the
database table.

The arrows between the four entity classes
above represent associations/relationships between the different
entities. These are typically modeled using primary-key/foreign-key relationships
in the database. The direction of the arrows on the design-surface
indicate whether the association is a one-to-one or one-to-many
relationship. Strongly-typed properties will be added to the entity
classes based on this. For example, the Category class above has a
one-to-many relationship with the Product class. This means it will have
a "Categories" property which is a collection of Product objects
within that category. The Product class then has a "Category"
property that points to a Category class instance that represents the Category
to which the Product belongs.

The right-hand method pane within the LINQ to
SQL design surface above contains a list of stored procedures that
interact with our database model. In the sample above I added a single
"GetProductsByCategory" SPROC. It takes a categoryID as an
input argument, and returns a sequence of Product entities as a result.
We'll look at how to call this SPROC in a code sample below.